The invention relates to a method of manufacturing a semiconductor device in which in an elongate reactor monocrystalline material is grown epitaxially on disc-shaped monocrystalline substrates from a gas flow in the longitudinal direction of the reactor. During the epitaxial growth in the reactor a temperature gradient is maintained in the gas flow in the direction of the gas flow between a cross-section upstream of the gas flow where a first extreme temperature prevails and a cross section downstream of the gas flow where a second extreme temperature prevails. During the epitaxial growth the substrates are present in a temperature range between the extreme temperatures, and epitaxial growth takes place at different temperatures. The invention also relates to a semiconductor device manufactured by means of the method.
Epitaxial treatments are often used in the manufacture of semiconductor devices. In this manufacture it is an important problem to obtain epitaxial layers of a sufficiently homogeneous thickness.
It has been found that the growth rate of an epitaxial layer deposited from the gaseous phase is only slightly dependent on the temperature at high temperatures and is strongly dependent on the temperature at low temperatures. This means that at high temperatures diffusion in the gaseous phase is decisive of the growth rate and at low temperatures it is surface reactions which are decisive. The temperature must always be so high that the surface mobility is sufficient to obtain monocrystalline layers on monocrystalline substrates.
The above-described relationship between growth rate and temperature depends on the overall pressure.
At lower overall pressure the diffusion constant is larger and hence the diffusion is decisive to a smaller extent of the growth rate and the temperature over which the growth rate is determined by surface reactions is wider.
If the growth rate is determined by surface reactions the homogeneity of the thickness of the deposited layer is very good.
Although at lower pressures the growth rate is determined by surface reactions, over a wide temperature range the temperatures in said range are not yet high enough to obtain monocrystalline epitaxial layers of a good quality and with a reasonable growth rate.
Therefore, normally, only polycrystalline layers can be obtained in the said temperature range with a sufficient homogeneity of the layer thickness.
If, in order to obtain monocrystalline layers, high temperatures are used, the growth rate is determined by diffusion in the gaseous phase and the homogeneity of the thickness of the deposited layer is often insufficient.
This inhomogeneity is not removed in a method of the kind mentioned in the opening paragraph as described in U.S. Pat. No. 3,316,121 and in which the substrates on which growth has to be effected are placed in a temperature gradient which is adjusted so that, viewed in the direction of the gas flow, the reaction rate increases so as to level out the influence of the depletion in the gas flow of material to be grown on the growth rate. Moreover, this influence is substantially absent at higher temperatures at which the growth rate is determined by diffusion.